The NSABP is a cooperative group that had its start in 1958, but was officially formed in 1971, to conduct clinical trials in breast and colorectal cancer research. The National Cancer Institute is the primary source of funding for NSABP member institutions to conduct NSABP clinical trials. Current membership includes research sites at nearly 1,000 medical centers in the United States, Canada, Peurto Rico, Ireland, and Australia.

The NSABP has played a vital role in improving the treatment of women with breast cancer and has made many contributions in the management of colon and rectal cancers. During its nearly 50-year history, more than 110,000 women and men were enrolled in NSABP clinical trials, and results of NSABP studies have had a major impact on both the clinical care and the biological understanding of cancer.

The NSABP sponsored the Breast Cancer Prevention Trial, a landmark breast cancer study that determined the effectiveness of tamoxifen in preventing the occurrence of breast cancer in women at high risk for the disease.